Method of manufacturing glass reinforced concrete building products

ABSTRACT

Reinforced concrete building products are manufactured using a two-part mould (2, 3), the two parts being hinged together about an axis (4) which is adjacent an edge of each part-mould (2, 3). Glass-reinforced concrete is applied to each part-mould (2, 3), then allowed to partly dry before the part-moulds (2, 3) are folded together to produce a finished product.

This invention relates to a method of manufacturing glass reinforcedconcrete building products. It relates particularly but not exclusivelyto a method of manufacturing glass reinforced concrete panels suitablefor use as acoustic barriers.

Glass reinforced concrete has been used for several years as a buildingmaterial in such applications as partitioning, linings, fascias,facades, cladding, curtain walling, spandrels, fencing and other similarsuch applications. Glass reinforced concrete (hereinafter referred to as"GRC") is made from a combination of Portland cement and silica sandreinforced with glass fibre (usually alkaline resistant glass strands).

GRC is known to be good acoustic barrier material because of its abilityto reduce sound transmission. For example, a typical 10 mm thickness ofGRC has a sound transmission loss of about 30 dB. GRC is particularlysuitable for sound damping applications adjacent highways and motorways,but its use has not been fully exploited because the glass fibres in GRCare sharp, GRC tends to be rough, and adequate methods of manufacturingusing GRC have not been developed.

In the particular application of roadside noise damping, it has beendiscovered that effective results are achieved if a wall comprised ofGRC panels is placed beside the road. Each of the panels is constructedin such a way that the panel has reflective, dispersive or absorptivecharacteristics, or a combination of these. It is desirable that thepanels in the wall be arranged contiguously.

The acoustic properties of individual GRC panels will depend to someextent upon the construction of those panels. Thus, while a suitablepanel may be comprised of two or more pieces screwed or glued together,it is more desirable that a panel be formed in a single mouldingoperation. This is because joints have an inherently deleterious effecton the acoustic properties of a panel, and the securing together of GRCsheets is a labour intensive task.

It is a known technique for cast-moulding to use a two-part mouldwherein, after the object in the mould has hardened, the parts of themould are separated and the object can be removed. However, such amoulding technique is generally suitable only for solid or substantiallysolid objects. The present invention develops the known cast-mouldingtechnique to create a new method of cast-moulding substantially hollowobjects.

It is an object of this invention to provide a method of manufacturingGRC panels. Another object of this invention is to provide a method ofmanufacturing GRC panels in such a way that the GRC panels are suitablefor contiguous installation. A further object of this invention is toprovide a method of manufacturing a single piece GRC panel.

According to one aspect of the present invention, there is provided amethod of manufacturing a glass reinforced concrete building product,comprising:

(a) providing a two-part mould, wherein the two parts are hingedtogether about an axis which is adjacent an edge of each of the twoparts of the mould;

(b) covering both parts of the mould including the hinge with at leastone layer of glass reinforced concrete;

(c) folding the two parts of the mould together; and

(d) leaving the mould for a period of time to allow the glass reinforcedconcrete to harden, forming a single building product.

As a preferred feature, step (b) includes the placing of one or moreadditional mould elements at or near one or more edges of one or bothparts of the mould, in order to cause one or more edge portions of thefinished building product to have a particular shape. It is preferredthat the edge-shaping be accomplished by use of this technique ratherthan by shaping after the GRC has hardened because it is difficult tomodify the shape of hardened GRC, and such modifications tend to lead toweakness in the finished products.

According to another aspect of the present invention, there is provideda two-part mould wherein the two parts are hinged together about an axiswhich is adjacent an edge of each of the two parts of the mould. Thismould is suitable for use in the method previously described.

According to a further aspect of the invention, there is provided ahollow GRC panel made according to the method previously described. Thepreferred panel has four edges, with channels extending along threeedges and a ridge extending along the fourth.

The preferred ratio of sand to cement for usage in creating GRC panelsis from 1:1 to 1:2, with the most preferred ratio being 1:2. Thepreferred working range ratio for water to cement is 0.32 to 0.38, withthe most preferred value being 0.35.

The preferred percentage of glass fibre present in the component mix isfrom 2.5 to 6.3. The most preferred range is 5.0 to 5.3%.

The preferred glass fibre length range is from 10 to 50 mm. The mostpreferred range is 35 to 38 mm.

Example embodiments of the method of the present invention areillustrated in the attached drawings.

FIG. 1 shows a foldable mould in its laid flat position.

FIG. 2 shows the same foldable mould with channel formers attached.

FIG. 3 shows the foldable mould in its folded state.

FIG. 4 shows a dispersive GRC panel constructed using the foldable mouldof FIG. 1.

FIG. 5 shows a half-mould with hingedly attached channel formers.

FIGS. 1 to 4 illustrate steps in the construction of a dispersive GRCpanel using a foldable mould. A foldable mould, designated generally as1, comprises two half moulds 2 and 3. The two half moulds 2 and 3 areconnected at hinged connection 4. Foldable mould 1 is supported in alaid flat position on trestle table 5 by means of supporting pins 6.

Foldable mould 1 is preferably cleaned by scraping away excess GRC fromprevious moulding operations and blowing air over the mould to eliminatedust. The mould is preferably also oiled in preparation for the mouldingoperation.

The preferred method comprises applying a mist coat of cement over theentire mould, followed by the application of one coat of GRC over theentire mould, including the area about hinged connection 4. The GRC isthen rolled by means of a hand-held roller and surplus GRC around theedges of the mould is folded back into the mould with a trowel.

Channel formers 7 are placed around the edges of one of the half moulds3 as illustrated in FIG. 2. A mist coat of cement is applied to thechannel formers, followed by a second coat of GRC which is appliedaround the base, sides and top of the channel formers. A substantialslurry coat is applied around the edges of the mould and the mould isallowed to sit for 5 to 10 minutes in order to allow the GRC to stiffen.

The stiffening process may be assisted in between the application ofdifferent layers or after the final layer by the use of aconcrete-hardening acceleration agent, such as the one sold byCementaids (International) Pty Ltd under the trade name RAPIDARD.

The two half moulds are then folded together about hinged connection 4so that the GRC inside one half-mould contacts the GRC inside the otherhalf-mould around the edges of the mould and the GRC inside the mouldforms a hollow box or panel shape. Further GRC or cement may be appliedas the two half-moulds are brought together. The mould is then clampedin a closed position, as illustrated in FIG. 3.

This method, which results in the formation of a hollow, single-pieceGRC panel having four edges, ensures that the panel has a reasonableresistance to shear forces because one of the edges (namely the edgenearest hinged connection 4) is fully reinforced by glass fibres.

The mould is held closed for approximately 12 hours, after which timethe GRC will have set sufficiently to allow for removal from the mould.Protrusions may then be removed, and indentations may be patched asrequired. Completed panels are preferably cured for a period such asseven days.

FIG. 4 illustrates a completed dispersive GRC panel which in this casehas a ridge 8 on its top side and channels 9 on its other sides.

FIG. 5 illustrates a half-mould 10 which has hingedly attached channelformers 11. This half-mould is suitable for use in the method previouslydescribed.

According to an alternative embodiment using the half-mould 10 of FIG.5, a mist coating of cement is first applied to the mould, followed bythree coatings of GRC at 5% glass. A hand-held roller is used toconsolidate the GRC after each coating.

Channel formers 11 are then rotated into position around their hingedconnections and a mist coating of cement is applied to all the areasthat have not yet been sprayed, with extra amounts of cementconcentrated towards the corners.

Three further coatings of GRC are then applied, so that the GRC has anaverage thickness of about 10 mm. The method then proceeds in the samemanner as the previously described embodiment.

The use of channel formers in the method of the present inventionresults in the creation of GRC panels with channels along up to 3 edgesand, preferably, a ridge along the fourth edge. Panels having such ashape are particularly advantageous as they allow for easy and aestheticinstallation on site.

The preferred technique for installing a panel in a noise-deflecting orabsorbing application involves installing vertical posts one panel-widthapart, then sliding the panel down over the posts, with the panel'sridge edge upwards and the two side edge channels each accommodatinghalf of a vertical post. The top ridge edge of the panel fits into thebottom channel edge of the panel above. The other half of each verticalpost is accommodated in a side edge channel of an adjacent panel. It isthus possible to form a substantial sound barrier of contiguous panels,providing an effective acoustic seal.

It is to be understood that various alterations, modifications and/oradditions may be introduced into the constructions and arrangements ofparts previously described without departing from the spirit and ambitof the invention.

As will be seen from the foregoing, the present invention providesimprovements in the usage of GRC in the construction of concrete panels.In particular, it provides a method for producing a GRC panel which ishollow and substantially smooth, as well as having resistance to shearforces.

I claim:
 1. A method of manufacturing a glass reinforced concretebuilding product, comprising:(a) providing a two-part mould, wherein thetwo parts are hinged together about an axis which is on an edge of eachof the two parts of the mould by a hinge; (b) covering both parts of themould including the hinge with at least one layer of glass reinforcedconcrete, the glass reinforced concrete being applied across the hingefrom one part of the mould to the other; (c) folding the two parts ofthe mould together; and (d) leaving the mould for a period of time toallow the glass reinforced concrete to harden, forming a single buildingproduct.
 2. A method according to claim 1, wherein step (b) furtherincludes a step of applying cement which does not contain glass and aconcrete-hardening acceleration agent.
 3. A method according to claim 1,wherein at least one additional mould element is placed proximate to atleast one edge of at least one said part of the mould during step (b),in order to cause at least one edge portion of a finished buildingproduct to have a particular shape.
 4. A method according to claim 3,wherein the additional mould element is attached to the mould by atleast one hinge.
 5. A method according to claim 3, wherein theadditional mould element causes the finished building product to have achannel along at least one edge.
 6. A method according to claim 5,wherein the finished building product has four edges, the additionalmould element causes the building product to have channels along threeof the edges, and a shape of the mould in an area of the hinge causes aridge along the fourth edge.